1. Field of Invention
The present invention relates to a wiring pattern for a liquid crystal display in which unevenness is not noticeable, a liquid crystal display, and an electronic equipment using the liquid crystal display.
2. Description of Related Art
In general, a color liquid crystal display in an active matrix system includes a plurality of pixel electrodes, a device substrate on which these pixel electrodes are provided with nonlinear (switching) devices, an opposing substrate on which counter electrodes opposed to the pixel electrodes and color filters are formed, and liquid crystal filled between the two substrates. Each pixel corresponds to one of three primary colors, R (red), G (green), and B (blue).
With this arrangement, when a selection signal is applied to scanning lines, the switching devices enter a conducting state. When a data signal is applied to data lines in the conducting state, a predetermined charge is accumulated in liquid crystal layers including the pixel electrodes, the counter electrodes, and the liquid crystal between the pixel electrodes and the counter electrodes. When the switching devices enter an off state after the charge has been accumulated, the accumulated charge in the liquid crystal layers is maintained if the resistance of the liquid crystal layers is sufficiently high. Accordingly, when the switching devices are driven so as to control the amount of charge to be accumulated, alignment of the liquid crystal varies according to each pixel, thus displaying predetermined information. It is only necessary to accumulate charge in each liquid crystal layer for a partial period. Therefore, time-division multiplexing driving in which the pixels share the scanning lines and the data lines is made possible by selecting the scanning lines using time-sharing.
Concerning the nonlinear devices, they are broadly classified into a three-terminal nonlinear device, such as a thin-film transistor (TFT), and a two-terminal nonlinear device, such as a thin-film diode (TFD). The latter, that is the two-terminal nonlinear device, is advantageous in that short circuit failure does not occur in theory since there are no intersections in the wiring and that a film deposition process and a photolithography process are shortened. If the two-terminal nonlinear device is to be employed as the nonlinear device, the two-terminal nonlinear device can be connected to either one of the scanning line and the data line. Here, it is assumed that the two-terminal nonlinear device is connected to the data line.
In contrast, concerning arrangements of the color filters in the liquid crystal display, those shown in FIGS. 10(a) to (d) are known. Of these arrangements, the arrangement shown in FIG. 10(a) is referred to as an RGB stripe arrangement or a trio arrangement, and is suitable for a computer display for displaying characters and straight lines. In comparison with the arrangements shown in FIGS. 10(b) to (d), the effective resolution of the arrangement shown in FIG. 10(a) is not so high.
The next arrangement shown in FIG. 10(b) is referred to as an RGGB mosaic arrangement. Since this arrangement has a greater number of G pixels having a high visibility factor, it is generally said that this arrangement has high resolution. However, the arrangement is not necessarily evaluated highly by subjective evaluation experiments. Furthermore, the RGGB mosaic arrangement has a fewer number of B and R pixels. Thus, this arrangement has a drawback in that roughness of an image is noticeable when the viewing distance is short.
The arrangement shown in FIG. 10(c) is referred to as an RGB mosaic arrangement. In this arrangement, a difference in display quality occurs between a rightward-rising diagonal and a leftward-rising diagonal. This generates diagonal noise in an overall image, and, in particular, the noise is noticeable when the number of pixels of a screen is small.
The arrangement shown in FIG. 10(d) is referred to as an RGB delta arrangement, and has a horizontal resolution that is 1.5 times that of the mosaic arrangement. It is said that the RGB delta arrangement is disadvantageous in displaying the contour of an image. Generally, however, the RGB delta arrangement is evaluated highly by subjective evaluation experiments. It is thus suitable for achieving a high definition color liquid crystal display. Hereinafter, drawbacks involved in employing the RGB delta arrangement are discussed.
When the color filters are arranged in the RBG delta arrangement, a wiring pattern of connecting lines (one of the data lines and the scanning lines, and hereinafter simply referred to as lines) to be connected to the pixel electrodes that will be the base of these pixels is discussed below. Concerning the wiring pattern, there is a system in which two of the three RGB colors share a single line, as shown in FIGS. 11(a) and (b). Specifically, line 1 (1xe2x80x2) is shared by R and G, line 2 (2xe2x80x2) is shared by G and B, and line 3 (3xe2x80x2) is shared by B and R. This system has a drawback in that unevenness occurs when displaying solid patterns of C (cyan), M (magenta), and Y (yellow) that are in a complementary-color relation with the RGB colors, that is, when displaying a relatively large area in a single color.
Regarding the principle of this development of unevenness, the case of displaying cyan is discussed. In this case, a liquid crystal display in a normally white mode displays white (off) in a no-applied-voltage state. When displaying cyan, the R pixels must be black (on) and the G and B pixels must be white. Thus, it is only necessary to write to the R pixels. Because the G pixels on even rows are connected to line 1 (1xe2x80x2), potentials of these G pixels tend towards potentials when writing to the R pixels. In contrast, the G pixels on odd rows are connected to line 2 (2xe2x80x2), and potentials of these G pixels are substantially independent of the potentials when writing to the R pixels. Similarly, because the B pixels on odd rows are connected to line 3 (3xe2x80x2), potentials of these B pixels tend towards the potentials when writing to the R pixels. In contrast, the B pixels on even rows are connected to line 2 (2xe2x80x2), and potentials of these B pixels are substantially independent of the potentials when writing to the R pixels.
As a result, an effective voltage value applied to the G pixels on the even rows and an effective voltage value applied to the G pixels on the odd rows are different from each other. In addition, an effective voltage value applied to the B pixels on the odd rows and an effective voltage value applied to the B pixels on the even rows are different from each other. Accordingly, a difference in gray level occurs every other row. The same drawback occurs when displaying magenta and yellow, and a difference in gray level occurs between odd rows and even rows.
In other words, the difference in gray level becomes uneven in the column direction. Specifically, the B and G pixels which are influenced by writing to the R pixels are alternately shifted by half a pitch of the pixels, and are connected in the column direction. In contrast, the B and G pixels which are not influenced by writing to the R pixels are alternately shifted by half a pitch in a similar manner, and are connected in the column direction. This generates a difference in gray level between the cyan in the column direction of the former pixels and the cyan in the column direction of the latter pixels. Hence, unevenness in the column direction is caused.
In order to prevent such unevenness from occurring, it is necessary to obtain a wiring pattern in which potentials when writing to pixels of a certain color do not influence the potentials of pixels of other colors. To this end, as shown in FIG. 12, it is possible to propose a system in which a single line is shared by only a single color. Specifically, line 4 is shared by G, line 5 is shared by B, and line 6 is shared by R.
With this wiring pattern, there is a problem in that unevenness occurs when displaying solid color patterns in cyan, magenta, and yellow due to a reason that is different from the above-described reason. The principle of this development of unevenness is discussed below. Concerning the wiring pattern, the G pixels on the odd lines are encircled by a xe2x80x9cUxe2x80x9d shape by line 5 for writing to the B pixels. In contrast, concerning the G pixels on the even rows, they are similarly encircled by a xe2x80x9cUxe2x80x9d shape by line 6 for writing to the R pixels. Specifically, concerning the G pixels, there are two types: one capacitively coupled to line 5 and the other capacitively coupled to line 6. Similarly, concerning the B pixels, there are two types one capacitively coupled to line 4 and the other capacitively coupled to line 6.
As in the above-described case, when displaying, for example, cyan in the normally white mode, the R pixels must be black and the G and B pixels must be white. Hence, it is only necessary to write to the R pixels. If a write voltage is applied to line 6 so as to write to the R pixels, the gray level in the G pixels on the even rows and the B pixels on the odd rows varies since they are capacitively coupled to line 6. In contrast, concerning the G pixels on the odd rows and the B pixels on the even rows, the gray level does not vary since they are substantially independent of the potential of line 6. This results in a difference between the gray level in the G pixels on the even rows and the B pixels on the odd rows and the gray level of the G pixels on the odd rows and the B pixels on the even rows, thus causing unevenness. The same drawback occurs when displaying magenta and yellow.
In view of the above circumstances, it is an object of the present invention to at least provide a wiring pattern of a liquid crystal display in which unevenness is prevented from becoming noticeable as much as possible, thereby improving the quality of a display image, to provide a liquid crystal display, and to provide an electronic equipment using the liquid crystal display.
To this end, according to a first exemplary embodiment of this invention, a wiring pattern for a liquid crystal display is arranged by shifting pixel electrodes corresponding to pixels displaying different colors by substantially half a pitch for every row. Conduction lines shared by the pixel electrodes in the column direction are connected to the pixel electrodes corresponding to the same color. Parasitic capacitances of the pixel electrodes are made uniform in each pixel.
In order to make the parasitic capacitances of the pixel electrodes uniform in each pixel, the periphery of each pixel electrode may be encircled by the conduction line connected to each pixel electrode. Alternatively, the periphery, apart from a side opposed to the adjacent conduction line, of each pixel electrode may be encircled by the conduction line connected to each pixel electrode. With these arrangements, pixels on even rows and pixels on odd rows are such that a write potential to pixels of a certain color does not influence a potential of pixels of another color. In addition, the gray level of pixels does not vary every row. Hence, it is possible to display an image of high quality.
According to a second exemplary embodiment of this invention, a liquid crystal display includes pixel electrodes corresponding to pixels displaying different colors. The pixel electrodes are provided corresponding to intersections of scanning lines arranged in the row direction and data lines arranged in the column direction. The pixel electrodes are shifted by substantially half a pitch for every row and are thus arranged. Conduction lines shared by the pixel electrodes in the column direction are connected to the pixel electrodes corresponding to the same color. Parasitic capacitances of the pixel electrodes are made uniform in each pixel. Since the liquid crystal display with this arrangement uses the above-described wiring pattern, it is possible to display an image of high quality.
According to the second exemplary embodiment of this invention, it is preferable that the data lines be connected to the pixel electrodes through switching devices. The switching devices may be thin-film diode devices including conductor/insulator/conductor. Accordingly, it is possible to obtain a uniform display image even when the thin-film diode devices in which it is difficult to form storage capacitances in parallel with the pixel electrodes are employed.
According to a third exemplary embodiment of this invention, an electronic equipment includes a liquid crystal display having pixel electrodes corresponding to pixels displaying different colors. The pixel electrodes are provided corresponding to intersections of a plurality of scanning lines arranged in the row direction and a plurality of data lines arranged in the column direction. The pixel electrodes are shifted by substantially half a pitch for every row and are thus arranged. Conduction lines shared by the pixel electrodes are connected to the pixel electrodes corresponding to the same color. Parasitic capacitances of the pixel electrodes are made uniform in each pixel. Concerning such an electronic equipment, there is an information terminal unit, such as a notebook-size personal computer, a pager, or a cellular phone.